Legal Question in Landlord & Tenant Law in Louisiana

I do not believe the law sets any maximum amount for a late fee, except that it cannot be an amount that is so high that it would be against public policy, which would void the contract. The late fee is set up in the lease and the tenant is not required to sign it. The lease is "the law between the parties" and any court would be loathe to disregard its terms, since both parties knew the terms and agreed to them upon signing the lease.

I can say that a "usual" late fee is anyhwere from $50-$100. I have also seen late fees of 10%-15% of the monthly rental amount. Those are "standard", but there is no law setting that as the "standard".

It is VERY important to read your lease before you sign it and bring any problems up to the landlord before you sign. Once you sign it, you have agreed to its terms. This leaves you little room to argue that its terms are unduly burdensome later.